The use of RFID tags are quickly gaining popularity for use in the monitoring and tracking of an item. RFID technology allows a user to remotely store and retrieve data in connection with an item utilizing a small, unobtrusive tag. As an RFID tag operates in the radio frequency (RF) portion of the electromagnetic spectrum, an electromagnetic or electrostatic coupling can occur between an RFID tag affixed to an item and an RFID tag reader. This coupling is advantageous, as it precludes the need for a direct contact or line of sight connection between the tag and the reader.
Inverted F antennas have been used in wireless communications systems including mobile telephones, pagers, Global Positioning System (GPS), wireless LAN, WiFi, aircraft, locomotives, vehicles, radiolocation devices etc. Inverted-F antennas typically include a linear (i.e., straight) conductive element, e.g. a wire, that is maintained in spaced apart relationship with respect to a ground plane. They are especially useful where a low profile antenna is needed, one that does not stand tall above communications device, or mobile platform.
However, inverted F antennas have rarely if ever been implemented in RFID devices. This may be due to the standard configuration in which the feed line to the radiating element traverses the ground plane. Further, most inverted-F antennas are designed to match a 50 Ohm impedance, meaning that they will not function optimally if matched to an impedance that is not standard, e.g., 50 Ohms.
What is therefore needed is new design for inverted F antennas, as well as RFID devices implementing them.